Diamond protective coatings for optical components

The use of polycrystalline diamond films as protective coatings on IR materials has been highlighted as a major application of CVD diamond technology. However, those materials which would benefit most from diamond coatings, such as ZnS and Ge, possess vastly different thermomechanical properties. The severe technological problems which exist have prevented commercialization to the levels achieved by heat sinks and cutting tools.

We have been working for some time on the direct deposition of diamond onto protected ZnS windows and have extended our process to include other IR materials. By employing void-free protective interlayers we have produced diamond films up to 1 μm thick on planar interlayers on ZnS. Lithographic substrate patterning has been used to exceed this barrier and increase the achievable thickness towards the levels required for true protection from water drop or particulate erosion. Deposition onto sapphire substrates has permitted considerable progress in overcoming mechanical problems in isolation from chemical problems present with ZnS in an aggressive plasma.

The aspects of substrate preparation, adhesion and stress relief are discussed. The optical and structural properties of diamondcoated samples are presented.